Increasingly, the drilling of oil and gas wells is no longer a matter of drilling a vertically straight bore hole from the surface to the desired hydrocarbon zone. Rather, technology and techniques such as directional drilling have been developed to drill lateral or sometimes upwardly sloping well bores. It is often not economically feasible during such drilling operations to withdraw the drilling apparatus to add another discrete length of jointed drill pipe when necessary. Therefore, tools and methods have been developed for drilling bore holes using coiled tubing, which is a single length of continuous, unjointed tubing spooled onto a reel for storage in sufficient quantities to exceed the maximum length of the bore hole.
In well drilling applications, many circumstances can arise in which it is desirable to disconnect the tubing from the bottom hole assembly, such as, for example, when a bottom hole assembly gets stuck during drilling and the tubing must be disconnected from the bottom hole assembly to facilitate fishing, jarring, or other operations.
When application of a torque on the tubular members is permissible, traditional disconnection means such as threaded connections are frequently acceptable. However, when using non-rigid tubing such as coiled tubing, a torque can not be applied to disconnect the tubing from the drilling apparatus, and an axial disconnection means must be utilized. Pre-installation of an axial release device between the tubing and the bottom hole drilling assembly can provide a means to disconnect tubular members downhole if and when disconnection becomes necessary.
A variety of axial disconnect devices have been developed for use downhole, some of which use hydraulic or electrical lines that extend from the surface to actuate a piston and cause a release. One such device described in U.S. Pat. No. 5,323,853 includes redundant releasing mechanisms depending alternatively on either hydraulic or electrical actuation of a piston. The additional lines and cables run inside the well bore that are required to actuate this device have the disadvantage of creating an obstruction to fluid flow during normal drilling operations.
Another type of known release device depends for actuation on directing fluid flow so as to create backpressure and actuate a piston. U.S. Pat. No. 5,718,291 describes one such release mechanism that depends for actuation on either the use of backpressure created by flow through the device, or if flow is prevented, the use of built-up pressure within a passage in the device. In the first mode, backpressure created by flow through a restrictor above a shiftable sleeve overcomes a biasing spring to move the sleeve through a J-slot assembly until a passage is obstructed. Thereafter, pressure buildup in a second passage overcomes a shear pin, causing a piston to move and release dogs that lock two segments of the device together. If flow is prevented, pressure buildup in the second passage causes the piston to move against the shifting sleeve to overcome the force of the spring and selectively move the sleeve through the J-slot assembly. A disadvantage of this device is that aligning the sleeve properly to engage the top of the J-slot assembly is cumbersome, requiring that pressure be created and removed by turning pumps on and off from the surface.
Still another conventional release device depends for actuation on dropping a ball into a well from the surface, sealing a flow passage, and building up pressure behind the ball to cause a disconnection. One such ball-drop release device is described in U.S. Pat. No. 5,419,399 and includes a housing with a slideable piston disposed within and releasably connected to the housing by shear screws. A ball is dropped into the well from the surface to seat with the upper end of the piston and block the flow passage, thereby creating pressure on a mandrel of the piston sufficient to overcome the shear screws. The mandrel moves downward such that keys align to fit into annular grooves on the mandrel to disengage notches, allowing the tubing to be disconnected from the drilling apparatus. A disadvantage of this device is that the operator must pull back or agitate the device to cause the keys to drop into the grooves should they fail to do so.
A further ball-drop release device is described in U.S. Pat. No. 5,526,888 and includes an upper and lower housing insertably connected and locked together by latch blocks, a slotted piston that operates the latch blocks, a pilot piston, and a lock-out mechanism operated by movement of the pilot piston. A sealing ball is dropped into the well and seats with the pilot piston to create a pressure differential sufficient to overcome shear pins, thereby allowing the pilot piston to axially shift downward. Movement of the pilot piston releases a lock-out mechanism such that the slotted piston extends axially to retract the latch blocks and thereby disconnect the upper and lower housings.
Release devices of the ball-drop variety have several advantages over other types of release devices. Namely, selective rather than inadvertent separation is ensured because the operator must drop a ball into the well bore to actuate the release mechanism. There are also no requirements for additional hydraulic cables or electrical lines to actuate the release mechanism, and there are no cumbersome alignment requirements.
However, conventional ball-drop release devices have some limitations. The release ball is typically only suited for actuating a release device in a vertically disposed well bore. The release ball commonly has a density greater than the drilling fluid density such that it drops down through the drilling fluid in a vertical well bore to land and seat on the ball sleeve, thereby sealing the flow passage. When the well bore is not vertical, it is difficult to dependably land and seat the ball on the ball sleeve, especially when the ball must climb up a chamfer in a reduced diameter section to reach the ball sleeve in a lateral or upwardly sloped well bore.
Additionally, prior ball-drop release devices prevent continued circulation of drilling fluid through the device after the release mechanism is actuated, and these devices are not designed to effectively resist drilling motor backup torque necessary to prevent the release mechanism from locking up in the event the drilling motor is installed near the release device.
The present invention overcomes the deficiencies of the prior art.